This invention relates to energy attenuation apparatus and more particularly to a new energy attenuation restrictor device for use in an energy attenuation apparatus adapted to convey liquid under pressure for the attenuation of pressure pulsations in the liquid and to a method for manufacturing a restrictor device. The restrictor device of the invention is especially useful in the energy attenuation apparatus of the hydraulic system of a power steering unit of a vehicle. The invention would also be suitable for other hydraulic systems.
In hydraulic systems where the operating liquid is circulated by a pump, the pulsations of pressure generated by the pump are transmitted through the conduits and result in noise and/or vibration being produced by the hydraulic liquid. In the case of power steering fluid in vehicles, such noise and/or vibration are caused, for example, when a vehicle is being operated at idle or very low speeds of movement such as barely moving into and out of a parking space where the wheels of the vehicle are being turned by the power steering mechanism. In those instances where the wheels are being turned with little or no rolling of the wheel, substantial noise and/or vibration (shudder) can be produced when the power steering fluid passes through the power steering mechanism from the power steering pump to the effective steering structure. Further background in this area can be found in U.S. Pat. No. 3,323,305 to Klees which is incorporated herein by reference thereto.
Devices are known for suppressing noise in exhaust gas mufflers. For example, U.S. Pat. No. 4,501,341 to Jones provides two side branch resonators, while U.S. Pat. No. 4,371,053 to Jones provides an apertured tube in a gas muffler housing. Systems are also known for controlling the resonation of pressure waves in fuel injection systems. For examples, U.S. Pat. No. 5,168,855 to Stone passes fluid through check valves that are provided with a flow restriction either directly therein or in a bypass line. U.S. Pat. No. 5,509,391 to DeGroot provides a spool valve assembly for controlling flow between inlet and outlet ports. Henderson et al., in U.S. Pat. No. 4,671,380, discloses a long and narrow tubular casing having a perforated tube extending therethrough. Finally, xe2x80x9cAcoustics of Ducts and Mufflersxe2x80x9d, by M. L. Munjal, describes an apertured resonator tube disposed in a tubular cavity for conveying gas.
Commonly assigned U.S. Pat. Nos. 6,073,656 and 6,123,108, both to Chen et al., the contents of which are incorporated herein by reference thereto, describe energy attenuation apparatus providing tubular means having an inlet opening for receiving liquid from the system, and an outlet opening for returning the liquid to the system, wherein an inlet conduit extends concentrically into the tubular means through the inlet opening such that an annular space is formed between the inlet conduit and the tubular means. In a portion of the inlet conduit disposed in the tubular means, the inlet conduit is provided with at least one aperture for introducing liquid from the inlet conduit into the annular space between the inlet conduit and the tubular means.
Applicants are not aware of any other teaching of transferring flow of liquid under pressure from one tube to another as a means of suppressing energy, especially where at least one of the tubes is provided with at least one hole.
It is an object of the present invention to provide an improved energy attenuation restrictor device for attenuating energy in a conduit that conveys liquid under pressure.
It is another object of the invention to provide a method for manufacturing an improved energy attenuation restrictor device for attenuating energy in a conduit that conveys liquid under pressure.
In a pressurized liquid system, such as a power steering system in an automobile, pressurized liquid is generated and transmitted through tubing, such as steel tubing, to a pressure line, a power steering gear, a fluid return line, a reservoir and finally back to the pump itself. During the generation and transmission of the fluid under pressure, pressure ripples are also generated and transmitted through the tubing. In order to reduce such pressure ripples before they reach the gear, and thereby eliminate or at least greatly reduce the power steering noise or vibration generated by the power steering pump, an energy attenuation device such as that described in the above commonly assigned U.S. Pat. Nos. 6,073,656 and 6,123,108 to Chen et al., is disposed in the pressure line between the power steering pump and the gear.
Currently, the restrictor device for attenuating energy, commonly referred to a tuning cable assembly, consists of a tuning cable which may be constructed of a metal or a polymeric material, and a metal fitting member annularly disposed around one end of the tuning cable and held in place by friction. This fitting member including the tuning cable is inserted into a metal support member which is crimped to hold the fitting member and the tuning cable in place in the metal support member. The tuning cable assembly anchored to the metal member is then inserted into a housing or, preferably a hose and kept in place by a metallic shell which is crimped onto the hose.
In the present invention, both the tuning cable and the fitting member of the restrictor device are manufactured from a polymeric material. Both parts may be made of the same plastic material or they may be made from different plastic materials. By using polymeric materials to manufacture both the tuning cable and the fitting member in accordance with the present invention, the inventive restrictor device is more conveniently recyclable, lower in cost, lighter in weight, and, more importantly, consists of fewer parts. In a particularly preferred and advantageous embodiment of the invention, the present restrictor device is manufactured in a single step in an injection molding machine wherein the tuning cable and the fitting member, are simultaneously molded together forming a unitary restrictor device.